Lower Cretaceous source rock evaluation and thermal maturity evolution of the Chagan depression, Inner Mongolia, Northern China

The Chagan depression has the greatest oil and gas exploration potential in the Yingen-Ejinaqi Basin, Inner Mongolia, northern China. In this paper, source rocks are evaluated and the thermal maturity evolution of typical wells and the primary source rocks is modeled using BasinMod 1D and Basinview software provided by Platte River Associates, Inc. The results show that the Chagan depression developed three sets of source rocks, including the Baiyingebi 1 and 2 Formations and Suhongtu 1 Formation. The Baiyingebi 2 Formation has been the most important source rock in the Chagan depression, dominated by the medium to high maturity source rocks with type II kerogen. This study also reveals that the thermal maturity evolution of source rocks is controlled by the paleogeothermal fields during the Yingen Formation depositional periods when the maximum maturity was reached. The Bayingebi 1 and 2 Formations both experienced the hydrocarbon generation peak and reached the medium to over mature stage. While the Suhongtu 1 Formation has only reached the low to medium mature stage with lower hydrocarbon generation potential. In addition, the source rocks thermal maturity evolution in the West sag is superior to that in the East sag. Therefore, the Bayingebi 2 Formation should be investigated for the oil exploration, and the Wuliji fault nose structural zone and central structural zone will remain the primary targets for the next exploration.